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Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.


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TL;DR: In this article, an 8nm cobalt ferrite particles of 8nm grain size were synthesized by coprecipitation technique and subsequently suitably heat treated to obtain higher grain sizes and experimentally observed changes in dc electrical conductivity and Curie temperature with heat treatment have been attributed to the changes in the cation distributions as obtained from the Mossbauer and extended x-ray absorption fine structure (EXAFS) measurements and to the grain size.
Abstract: Nanocrystalline cobalt ferrite particles of 8nm grain size were synthesized by coprecipitation technique and subsequently suitably heat treated to obtain higher grain sizes The experimentally observed changes in the dc electrical conductivity and Curie temperature with heat treatment have been attributed to the changes in the cation distributions as obtained from the Mossbauer and extended x-ray absorption fine structure (EXAFS) measurements and to the grain size The activation energies for conduction as determined from the Arrhenius plots suggest that the conductivity is due to hopping of both electrons and holes The observed decrease in conductivity when the grain size is increased from 8to92nm is clearly due to the predominant effect of migration of some of the Fe3+ ions from octahedral to tetrahedral sites, as is evident from in-field Mossbauer and EXAFS measurements But the higher conductivity of the 102 and 123nm particles compared to that of the 92nm particles is attributed to the higher grain

89 citations

Journal ArticleDOI
04 Feb 2014-ACS Nano
TL;DR: DNP-SENS experiments can be carried on many types of uniform colloidal nanomaterials containing NMR-active nuclei, in the presence of either hydrophilic (ion-capped surfaces) or hydrophobic (capping ligands with long hydrocarbon chains) surface functionalities.
Abstract: A particularly difficult challenge in the chemistry of nanomaterials is the detailed structural and chemical analysis of multicomponent nano-objects. This is especially true for the determination of spatially resolved information. In this study, we demonstrate that dynamic nuclear polarization surface-enhanced solid-state NMR spectroscopy (DNP-SENS), which provides selective and enhanced NMR signal collection from the (near) surface regions of a sample, can be used to resolve the core-shell structure of a nanoparticle. Li-ion anode materials, monodisperse 10-20 nm large tin nanoparticles covered with a ∼3 nm thick layer of native oxides, were used in this case study. DNP-SENS selectively enhanced the weak 119Sn NMR signal of the amorphous surface SnO2 layer. Mossbauer and X-ray absorption spectroscopies identified a subsurface SnO phase and quantified the atomic fractions of both oxides. Finally, temperature-dependent X-ray diffraction measurements were used to probe the metallic β-Sn core and indicated that even after 8 months of storage at 255 K there are no signs of conversion of the metallic β-Sn core into a brittle semiconducting α-phase, a phase transition which normally occurs in bulk tin at 286 K (13 °C). Taken together, these results indicate that Sn/SnOx nanoparticles have core/shell1/shell2 structure of Sn/SnO/SnO2 phases. The study suggests that DNP-SENS experiments can be carried on many types of uniform colloidal nanomaterials containing NMR-active nuclei, in the presence of either hydrophilic (ion-capped surfaces) or hydrophobic (capping ligands with long hydrocarbon chains) surface functionalities.

88 citations

Journal ArticleDOI
TL;DR: In this paper, hydrogen chemisorption on small silica-supported Pt clusters was investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and X-Ray absorption near-edge structure (XANES) spectrograms.
Abstract: Hydrogen chemisorption on small silica-supported Pt clusters was investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy. The clusters were found to exhibit a bulklike Pt first nearest neighbor (NN) distance (2.76 A) and low disorder while covered by chemisorbed hydrogen. In contrast, bare Pt clusters produced by heating in vacuo at 300 °C are characterized by a contracted Pt NN distance (2.66 A) and greater disorder. These effects are reversed by re-exposure of the bare Pt clusters to H2 at 25 °C. The metal−support interface is characterized by a short Pt−O distance, irrespective of the presence of chemisorbed hydrogen. An apparent L3 edge shift of 0.8 eV relative to bulk Pt is observed for the hydrogen-covered clusters. This shift is attributed to a decrease in the Pt L3 edge resonance (white line) intensity, as no corresponding shift is observed at the L2 edge. A hydrogen-related L2,3 XANES feature at 9 eV ap...

88 citations

Journal ArticleDOI
TL;DR: The EXAFS Debye-Waller factor shows that the clusters have 40% less thermal vibration than does the bulk, and a theory for this effect is presented, based on the change of bulk modulus with volume, the measured contraction of the clusters, and the softening effect of the surface modes.
Abstract: We performed optical absorption and temperature-dependent extended x-ray-absorption fine-structure (EXAFS) measurements on 55-atom gold clusters made by the Schmid process. The results are consistent with a fcc cuboctahedron structure, but with first-neighbor distances contracted by 0.075 \AA{}. The electronic properties, as detected by optical and x-ray absorption, are as expected for a small chunk of gold. The EXAFS Debye-Waller factor shows that the clusters have 40% less thermal vibration than does the bulk. We present a theory for this effect, based on the change of bulk modulus with volume, the measured contraction of the clusters, and the softening effect of the surface modes.

88 citations

Journal ArticleDOI
TL;DR: In this article, the nature of the active Ti species in TiCl3-doped NaAlH4, a promising hydrogen storage material, was studied as a function of the desorption temperature with Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, Ti Kedge Xray absorption near-edge structure (XANES) and XRD.
Abstract: The nature of the active Ti species in TiCl3-doped NaAlH4, a promising hydrogen storage material, was studied as a function of the desorption temperature with Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, Ti K-edge X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray diffraction (XRD). In the freshly prepared sample, Ti was amorphous and surrounded by 4.8 Al atoms divided between two shells at 2.71 and 2.89 A. In the next shell, 1.9 Ti atoms were detected at 3.52 A. It was concluded that 30% of Ti was incorporated into the surface of Al crystallites and 70% of Ti occupied interstitials in the NaAlH4 lattice, possibly forming trimeric, triangular Ti entities. After hydrogen desorption at 125 °C, NaAlH4 decomposed and the Ti−Al coordination number increased from 4.8 to 8.5. We propose that all Ti is incorporated into the surface layer of the formed Al. After the material was heated to 225 °C, the local structure of Ti, as inferred from EXAFS and XANES spectroscopy,...

88 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023110
2022264
2021156
2020164
2019164
2018151